The present invention relates to a fixing device utilized within an electrographic copying machine.
Typically, copying machines have a fixing unit, which is comprised of fixing rollers with either heated or cold pressure capability for permatizing the copy image. The rollers are applied together in a pair, having a particular degree of unit pressure at their nip. The pressure often depends on the type of copy paper utilized within the copying process of the copier.
Some fixing rollers are intentionally loaded together with relatively light pressure, such as 10 pounds per lineal inch. This is especially true of hot fusing devices, with internally heated rollers having silicone elastomer coatings on their exterior surfaces. Other fixing devices have rollers which are loaded together with pressure of substantial magnitude. The higher pressure capability fixing devices have rollers which are typically made from highly polished and hardened steels which are capable of withstanding loading of about 300 pounds per lineal inch.
And, the type of copy paper utilized in the copier, effects what degree of pressure is utilized within the fixing unit. For example, types of coated paper which receives the image directly such as zinc oxide, requires a lesser degree of pressure than bond paper. The bond paper typically requires the higher 300 pounds per inch loading.
In any case, it is important to recognize that it is desirable to keep the unit pressure loading between the fixing rollers at as low a magnitude as possible without sacrificing finished copy quality. A substantial pressure such as 300 pounds per inch magnitude obviously requires increased machine power to drive the rolls. And as demonstrated by prior art, creates a fixing unit assembly which is more difficult to construct because of the extra end to end loading required to bend the crossed rollers about each other, and the extra parts required to support and sustain the required loads.
As previously mentioned, the prior art discusses the means and the need to gain uniformly distributed lineal pressure across the full span of the fixing rollers.